Spin-transfer torque magnetic random-access memory (STT-MRAM) is a type of solid state, non-volatile memory that uses tunneling magnetoresistance (TMR) to store information. A MRAM system comprises an electrically connected array of magnetoresistive memory elements, referred to as magnetic tunnel junctions (MTJs). As is known in the art, a basic structure of a magnetic tunnel junction includes two thin ferromagnetic layers separated by a thin insulating layer through which electrons can tunnel. The spin-transfer torque (STT) phenomenon is realized in a MTJ structure, wherein one ferromagnetic layer (referred to as “magnetic free layer”) has a non-fixed magnetization, and the other ferromagnetic layer (referred to as a “magnetic pinned layer”, or “reference layer”) has a “fixed” magnetization. A MTJ stores information by switching the magnetization state of the magnetic free layer. When the magnetization direction of the magnetic free layer is parallel to the magnetization direction of the reference layer, the MTJ is in a “low resistance” state. Conversely, when the magnetization direction of the free layer is antiparallel to the magnetization direction of the reference layer, the MTJ is in a “high resistance” state. A magnetic tunnel structure can be fabricated with multiple magnetic, conductive and/or insulting layers, depending on the given application. For example, additional stacked layers may include two or more magnetic layers and two or more tunnel barrier layers, and other layers that are commonly implemented to construct other types of magnetic tunnel junction structures, e.g., double magnetic tunnel junction structures.
Conventional methods for fabricating embedded MRAM devices can lead to degraded performance of MRAM devices. For example, conventional methods for fabricating MRAM devices typically utilize a single etch process to etch a MTJ layer stack and bottom electrode layer down to an underlying dielectric layer to thereby form a MTJ structure and bottom electrode. With this etch process, an over-etch is performed to properly pattern the bottom electrode layer, which results in gouging of the underlying dielectric layer. In this instance, residual metallic material is re-deposited on the sidewalls of the MTJ structure (as a result of the etching of the MTJ layer stack and the bottom electrode layer), and residual dielectric material is re-deposited over the residual metallic material on the sidewalls of the MTJ structure (as a result of the etching of the underlying dielectric layer). The residual metallic material that is re-deposited on the sidewalls of the MTJ structure can result in junction shorts between metallic/magnetic layers within the MTJ structure.
While a cleaning etch process can be utilized to clean the residual material from the sidewalls of the MTJ structures, the cleaning etch process can be problematic as it is difficult to remove the metallic residue from the sidewalls of the MTJ structure with the metallic residue covered by the dielectric residue from the etching of the underlying dielectric layer. As such, the cleaning etch process must be performed for relatively long period of time and at a relatively high power to effectively remove the residual metallic material from the sidewalls of the MTJ structure. However, the cleaning etch process leads to further etching/gouging of the exposed surface of the underlying dielectric layer, which can lead to removal of the dielectric material in open areas outside the MRAM array and exposing metallic wiring of a lower interconnect level of a BEOL structure.